Are you trying to see if any 4 character sequence in Column C matches any 4 character sequence in Column B?
Peter|ABC Petez Ltd <--Match first four characters
Zeter|ABC Peter Ltd <--Match any four characters
(TonyJollans, Nice UDF btw!)
If you are just trying to see if only the first four characters on the text in Column B is found in Column C, then this sould work.
1) Case-sensitive
=IF(NOT(ISERROR(FIND(LEFT(B1,4),C1))),"Yup","Nope")
2) Not case-sensitive
=IF(NOT(ISERROR(SEARCH(LEFT(B1,4),C1))),"Yup","Nope")